It is most often used to provide IPv6 transit over an IPv4 network link when network address translation masquerades a private network with a single IP address that may change frequently because of DHCP provisioning by Internet service providers.
The protocol has the following features:[1] Many consumer networks are provisioned by Internet service providers using network address translation (NAT) which precludes[2][3][4] the usage of IP protocol 41 tunnels (IPv6 tunneled in IPv4 per either RFC 4213 or RFC 3056) unless they manually reconfigure their NAT setup.
In some cases, this is impossible as the NAT cannot be configured to forward protocol 41 to a specific host.
This situation limits the deployment of IPv6, which was meant to solve the problem of the disruption in end-to-end communications caused by NATs, which were created because of limited address space in the first place.
The remote host can determine whether a host supports AYIYA by querying for Domain Name System records and use public-key cryptography to authenticate the packets.